Compact head-mounted display system protected by a hyperfine structure

ABSTRACT

There is provided an optical system, including a light-transmitting substrate ( 20 ) having at least two external major surfaces and edges, an optical element for coupling light waves into the substrate ( 20 ) by internal reflection, at least one partially reflecting surface located in the substrate ( 20 ), for coupling light waves out of the substrate ( 20 ), at least one transparent air gap film ( 110 ) including a base ( 112 ) and a hyperfine structure ( 111 ) defining a relief formation, constructed on the base, wherein the air gap film is attached to one of the major surfaces of the substrate ( 20 ), with the relief formation facing the substrate ( 20 ) defining an interface plane ( 58 ), so that the light waves coupled inside the substrate ( 20 ) are substantially totally reflected from the interface plane ( 58 ).

FIELD OF THE INVENTION

The present invention relates to substrate-guided optical devices, andparticularly to devices which include a plurality of reflecting surfacescarried by a common light-transmissive substrate, also referred to as alight-guide element.

BACKGROUND OF THE INVENTION

One important application for compact optical elements is inhead-mounted displays (HMDs), wherein an optical module serves both asan imaging lens and a combiner, wherein a two-dimensional image sourceis imaged to infinity and reflected into the eye of an observer. Thedisplay source can be obtained directly from either a spatial lightmodulator (SLM) such as a cathode ray tube (CRT), a liquid crystaldisplay (LCD), an organic light emitting diode array (OLED), a scanningsource or similar devices, or indirectly, by means of a relay lens or anoptical fiber bundle. The display source comprises an array of elements(pixels) imaged to infinity by a collimating lens and is transmittedinto the eye of the viewer by means of a reflecting or partiallyreflecting surface acting as a combiner for non-see-through andsee-through applications, respectively. Typically, a conventional,free-space optical module is used for these purposes. As the desiredfield-of-view (FOV) of the system increases, however, such aconventional optical module becomes larger, heavier and bulkier, andtherefore, even for a moderate performance device, such as a system, isimpractical. This is a major drawback for all kinds of displays andespecially in head-mounted applications, wherein the system shouldnecessarily be as light and as compact as possible.

The strive for compactness has led to several different complex opticalsolutions, all of which on the one hand, are still not sufficientlycompact for most practical applications, and on the other hand, suffermajor drawbacks in terms of manufacturability. Furthermore, theeye-motion-box (EMB) of the optical viewing angles resulting from thesedesigns is usually very small, typically less than 8 mm Hence, theperformance of the optical system is very sensitive, even for smallmovements of the optical system relative to the eye of the viewer, anddoes not allow sufficient pupil motion for comfortable reading of textfrom such displays.

The teachings included in Publication Nos. WO 01/95027, WO 03/081320, WO2005/024485, WO 2005/024491, WO 2005/024969, WO 2005/124427, WO2006/013565, WO 2006/085309, WO 2006/085310, WO 2006/087709, WO2007/054928, WO 2007/093983, WO 2008/023367, WO 2008/129539, WO2008/149339, WO 2013/175465 and IL 232197, all in the name of Applicant,are herein incorporated by reference.

DISCLOSURE OF THE INVENTION

The present invention facilitates the exploitation of a very compactlight-guide optical element (LOE) for, amongst other applications, HMDs.The invention allows relatively wide FOVs together with relatively largeEMB values. The resulting optical system offers a large, high-qualityimage, which also accommodates large movements of the eye. The opticalsystem offered by the present invention is particularly advantageousbecause it is substantially more compact than state-of-the-artimplementations, and yet it can be readily incorporated, even intooptical systems having specialized configurations.

A broad object of the present invention is therefore to alleviate thedrawbacks of prior art compact optical display devices and to provideother optical components and systems having improved performance,according to specific requirements.

The invention can be implemented to advantage in a large number ofimaging applications, such as portable DVDs, cellular phones, mobile TVreceivers, video games, portable media players or any other mobiledisplay devices.

The main physical principle of the LOE's operation is that light wavesare trapped inside the substrate by total internal reflections from theexternal surfaces of the LOE. However, there are situations wherein itis required to attach another optical element to at least one of theexternal surfaces. In that case, it is essential to confirm that on theone hand, the reflection of light waves from the external surfaces willnot be degraded by this attachment, and on the other hand, that thecoupling-out and the coupling-in mechanisms of the light waves from andto the LOE will not be disturbed. As a result, it is required to add atthe external surfaces an angular sensitive reflective mechanism thatwill substantially reflect the entire light waves which are coupledinside the LOE and impinge on the surfaces at oblique angles, andsubstantially transmit the light waves which impinge on the surfacesclose to a normal incidence.

In previous inventions (e.g., described in Publication WO 2005/024491),a reflective mechanism, wherein an angular sensitive thin filmdielectric coating is applied to the surfaces of the LOE, has beenillustrated. According to the present invention, an alternativereflective mechanism that utilizes an air gap film, which comprises amoth-eye structure, is presented. Moths' eyes have an unusual property:their surfaces are covered with a natural nanostructured film whicheliminates reflections. This allows the moth to see well in the dark,without reflections, which give its location away to predators. Thestructure consists of a hexagonal pattern of bumps, each roughly 200 nmhigh and their centers are spaced apart about 300 nm. This kind ofanti-reflective coating works because the bumps are smaller than thewavelength of visible light, so the light “sees” the surface as having acontinuous refractive index gradient between the air and the medium,which decreases reflection by effectively removing the air-lensinterface. Practical anti-reflective films have been made by humansusing this effect, being a form of bio-mimicry. Moth eye replicas showthat reflectance for normally incident light is virtually completelyeliminated for these structures. Optical modeling and experiments withother shapes and dimensions of such dense uneven hyperfine periodicstructures prove that it is possible to suppress reflection in widerwavelength range (from UV to IR) and wider light incidence angles (0±60degrees).

According to the present invention the moth-eye film, or any similarhyperfine structure, is not utilized as anti-reflection film. Instead,the special hyperfine structure is exploited as the required angularsensitive reflective mechanism. When it is required to attach an opticalelement to the external surface of the LOE, an air gap film is cementedto the optical element such that the hyperfine structure faces the LOEafter the attachment. Therefore, when the coupled-in light waves insidethe LOE impinge on the hyperfine structure at different oblique angles,they “see” only the external part of the periodic structure. The actualrefractive index, which is “seen” by the incoming optical light wavesis, therefore, close to the refractive index of the air, and the totalinternal reflection mechanism is preserved. On the other hand, the airgap film is substantially transparent to the incoming light waves fromthe external scene or to the light waves which are coupled out from theLOE.

The invention therefore provides an optical system, including alight-transmitting substrate having at least two external major surfacesand edges, an optical element for coupling light waves into thesubstrate by internal reflection, at least one partially reflectingsurface located in the substrate, for coupling light waves out of thesubstrate, at least one transparent air gap film including a base and ahyperfine structure defining a relief formation, constructed on thebase, wherein the air gap film is attached to one of the major surfacesof the substrate, with the relief formation facing the substratedefining an interface plane, so that the light waves coupled inside thesubstrate are substantially totally reflected from the interface plane.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in connection with certain preferredembodiments, with reference to the following illustrative figures sothat it may be more fully understood.

With specific reference to the figures in detail, it is stressed thatthe particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only, and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention. The description taken with the drawings are to serve asdirection to those skilled in the art as to how the several forms of theinvention may be embodied in practice.

In the drawings:

FIG. 1 is a side view of an exemplary, prior art LOE;

FIG. 2 is a schematic diagram illustrating a prior art optical devicefor collimating input light-waves from a display light source;

FIG. 3 is a schematic diagram illustrating a prior art system forcollimating and coupling-in input light-waves from a display lightsource into an LOE;

FIG. 4 is a schematic diagram illustrating another prior art system forcollimating and coupling-in input light-waves from a display lightsource into a substrate, wherein the collimating module is attached tothe substrate;

FIG. 5 illustrates an exemplary embodiment of the present invention,wherein a negative lens is attached to an external surface of thelight-guide optical element, in accordance with the present invention;

FIG. 6 illustrates an exemplary embodiment of the present invention,wherein negative and positive lenses are attached to the externalsurfaces of the light-guide optical element, in accordance with thepresent invention;

FIGS. 7a and 7b are two- and three-dimensional schematic views of anexemplary embodiment of an air gap film, wherein a hyper-fine periodicstructure of transparent dielectric material arranged at a small pitchshorter than the wavelengths of the photopic region, is constructed on aflat transparent substrate;

FIGS. 8a and 8b respectively illustrate a side view and a top view of anexemplary air gap film;

FIGS. 9a and 9b respectively illustrate a side view and a top view of anexemplary air gap film for an internal cross section which is close tothe base;

FIGS. 10a and 10b respectively illustrate a side view and a top view ofan exemplary air gap film for an external cross section which is closeto the air;

FIG. 11 illustrates a side view of a light wave impinging on the upperside of a hyperfine structure at an oblique angle, in accordance withthe present invention;

FIG. 12 illustrates an air-gap film which is attached to the externalsurface of an LOE, wherein a coupled light wave impinges on theinterface surface between the LOE and the film, in accordance with thepresent invention;

FIGS. 13a and 13b respectively illustrate a front view of an eyeglassessystem and a top view of an LOE embedded between two optical lenses andassembled inside the eyeglasses frame, in accordance with the presentinvention;

FIGS. 14a, 14b and 14c respectively illustrate a non-monolithic opticalelement comprising an LOE embedded between a front positive lens and arear negative lens, mounted together inside a frame without adhesive, inaccordance with the present invention;

FIGS. 15a, 15b and 15c respectively illustrate an alternative method forembedding an LOE between two optical lenses, utilizing a peripheralbonding technique, in accordance with the present invention;

FIGS. 16a, 16b and 16c respectively illustrate an alternative method formonolithically embedding an LOE between two optical lenses, inaccordance with the present invention, and

FIGS. 17a, 17b and 17c respectively illustrate an LOE embedded betweentwo flat substrates and assembled inside a frame, in accordance with thepresent invention.

FIG. 18 illustrates an exemplary embodiment of the present invention,wherein the coupling-in as well as the coupling-out elements arediffractive optical elements, and

FIG. 19 illustrates an exemplary embodiment of the present invention,wherein the optical module is embedded in a hand-carried display system.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates a sectional view of a prior art optical systemincluding a planar substrate 20 and associated components (hereinafteralso referred to as an “LOE”), utilizable in the present invention. Anoptical means, e.g., a reflecting surface 16, is illuminated by lightwaves 18, which are collimated from a display of a light source (notshown). The reflecting surface 16 reflects incident light waves from thesource, such that the light waves are trapped inside the planarsubstrate 20 of the LOE, by total internal reflection. After severalreflections of the major lower and upper surfaces 26, 28 of thesubstrate 20, the trapped waves reach an array of selective partiallyreflecting surfaces 22, which couple the light out of the substrate intoa pupil 25 of an eye 24 of a viewer. Herein, the input surface of theLOE will be regarded as the surface through which the input light wavesenter the LOE, and the output surface of the LOE will be regarded as thesurface through which the trapped waves exit the LOE. In the case of theLOE illustrated in FIG. 1, both the input and the output surfaces are onthe lower surface 26. Other configurations, however, are envisioned inwhich the input and the image waves could be located on opposite sidesof the substrate 20, or when the light is coupled into the LOE through aslanted edge of the substrate.

As illustrated in FIG. 2, the s-polarized input light-waves 2 from adisplay light source 4 are coupled into a collimating module 6 throughits lower surface 30, which module is usually composed of a light-wavestransmitting material. Following reflection-off of a polarizingbeamsplitter 31, the light-waves are coupled-out of the substratethrough surface 32 of the collimating module 6. The light-waves thenpass through a quarter-wavelength retardation plate 34, reflected by areflecting optical element 36, e.g., a flat mirror, return to pass againthrough the retardation plate 34, and re-enter the collimating module 6through surface 32. The now p-polarized light-waves pass through thepolarizing beamsplitter 31 and are coupled out of the light-guidethrough surface 38 of the collimating module 6. The light-waves thenpass through a second quarter-wavelength retardation plate 40,collimated by a component 42, e.g., a lens, at its reflecting surface44, return to pass again through the retardation plate 34, and re-enterthe collimating module 6 through surface 38. The now s-polarizedlight-waves reflect off the polarizing beamsplitter 31 and exit thecollimating module through the upper surface 46. The reflecting surfaces36 and 44 can be materialized either by a metallic or a dielectriccoating.

FIG. 3 illustrates how a collimating module 6, constituted by thecomponents detailed with respect to FIG. 2, can be combined with asubstrate 20, to form an optical system. The output light-waves 48 fromthe collimating module 6 enter the substrate 20 through its lowersurface 26. The light waves entering the substrate 20 are reflected fromoptical element 16 and trapped in the substrate, as illustrated in FIG.2. Now, the collimating module 6, comprising the display light source 4,the folding prisms 52 and 54, the polarizing beamsplitter 31, theretardation plates 34 and 40 and the reflecting optical elements 36 and42, can easily be integrated into a single mechanical module andassembled independently of the substrate, even with non-accuratemechanical tolerances. In addition, the retardation plates 34 and 40 andthe reflecting optical elements 36 and 42 could be cemented together,respectively, to form single elements.

It would be advantageous to attach all the various components of thecollimating module 6 to the substrate 20, to form a single compactelement resulting in a simplified mechanical module. FIG. 4 illustratessuch a module, wherein the upper surface 46 of the collimating module 6is attached at the interface plane 58, to the lower surface 26 of thesubstrate 20. The main problem of this configuration is that theattaching procedure cancels the previously existing air gap 50(illustrated in FIG. 3) between the substrate 20 and the collimatingmodule 6. This air gap is essential for trapping the input light waves48 inside the substrate 20. The trapped light waves 48 should bereflected at points 62 and 64 of the interface plane 58. Therefore, areflecting mechanism should be applied at this plane, either at themajor surface 26 of the substrate 20, or at the upper surface 46 of thecollimating module 6. A simple reflecting coating cannot, however, beeasily applied, since these surfaces should also be transparent to thelight waves that enter and exit the substrate 20 at the exemplary points66. The light waves should pass through plane 48 at small incidentangles, and reflect at higher incident angles. Usually, the passingincident angles are between 0° and 15° and the reflecting incidentangles are between 40° and 80°.

In the above-described embodiments of the present invention, the imagewhich is coupled into the LOE is collimated to infinity. There areapplications, however, where the transmitted image should be focused toa closer distance, for example, for people who suffer from myopia andcannot properly see images located at long distances. FIG. 5 illustratesan optical system utilizing a lens, according to the present invention.An image 80 from infinity is coupled into a substrate 20 by a reflectingsurface 16, and then reflected by an array of partially reflectivesurfaces 22 into the eye 24 of the viewer. The (plano-concave) lens 82focuses the images to a convenient distance and optionally correctsother aberrations of the viewer's eye, including astigmatism. The lens82 can be attached to the surface of the substrate at its flat surface84. As explained above with regard to FIG. 4, a thin air gap must bepreserved between the lens and the substrate, to ensure the trapping ofthe image light waves 80 inside the substrate by total internalreflection.

In addition, in most of the applications related to the presentinvention, it is assumed that the external scene is located at infinity;however, there are professional or medical applications where theexternal scene is located at closer distances. FIG. 6 illustrates anoptical system for implementing a dual lens configuration, based on thepresent invention. Image light waves 80 from infinity are coupled into asubstrate 20 by a reflecting surface 16 and then reflected by an arrayof partially reflective surfaces 22 into the eye 24 of the viewer.Another image 86 from a close distance scene is collimated to infinityby a lens 88 and then passed through the substrate 20 into the eye 24 ofa viewer. The lens 82 focuses images 80 and 86 to a convenient distance,usually (but not necessarily always) the original distance of theexternal scene image, and corrects other aberrations of the viewer'seye, if required.

The lenses 82 and 88 shown in FIGS. 5 and 6 are simple plano-concave andplano-convex lenses, respectively, however, to keep the planar shape ofthe substrate, it is possible instead to utilize Fresnel lenses, whichcan be made of thin molded plastic plates with fine steps. Moreover, analternative way to materialize the lenses 82 or 88, instead of utilizingfixed lenses as described above, is to use electronically controlleddynamic lenses. There are applications where the user will not only beable to see a non-collimated image but also to dynamically control thefocus of the image. It has been shown that a high resolution, spatiallight modulator (SLM) can be used to form a holographic element.Presently, the most popular sources for that purpose are LCD devices,but other dynamic SLM devices can be used as well. High resolution,dynamic lenses having several hundred lines/mm are known. This kind ofelectro-optically controlled lenses can be used as the desired dynamicelements in the present invention, instead of the fixed lenses describedabove in conjunction with FIGS. 5 and 6. Therefore, in real time, a usercan determine and set the exact focal planes of both the virtual imageprojected by the substrate and the real image of the external view.

As illustrated in FIG. 6, it would be advantageous to attach the lenses82 and 88 to the substrate 20, to form a single, compact simplifiedmechanical module. Clearly, the main problem as hereinbefore described,is that the attaching procedure cancels the previously existing air gapbetween the substrate 20 and the lenses 82 and 88, which gaps areessential for trapping image light waves 80 inside the substrate 20. Thetrapped image light waves 80 should be reflected at point 90 of theinterface plane 84 and transmitted through the same plane at point 92.Therefore, a similar partially reflecting mechanism as described abovein relation to FIG. 4 should be applied at this plane.

To achieve the required partially reflecting mechanism, it is possibleto apply an angular sensitive thin film coating at the major surfaces ofthe substrate; however, the fabrication of this embodiment can becomplicated and expensive. An alternative way for realizing the requiredpartially reflecting mechanism is to attach a transparent air gap film110 to the major surfaces of the substrate, as illustrated in FIGS. 7aand 7b . The term air gap film relates to an optical device which has onits surface a hyper-fine periodic structure 111 of transparentdielectric material arranged at a small pitch shorter than thewavelengths of the photopic region, e.g., an optical device such asmoth-eye film having a dense (uneven) hyperfine periodic structure 111(hereinafter referred to as “relief formation”), which is constructed ona flat transparent substrate 112 (hereinafter referred to as “base” 112or “base film” 112). The height of the relief formation shouldpreferably (but not necessarily always) be less than 1 micron.

As seen in FIGS. 8a, and 8b , any cross section 121 parallel to thesurface of the air gap film 110 has a periodic formation, wherein theproportional portion of the dielectric material 123 in the reliefformation is changed gradually as a function from the film itself.

As further seen in FIGS. 9a, 9b and 10a and 10b , in the internal crosssection 124, which is close to the base film 112, i.e., the lowerportion of the hyperfine structure 111, the proportional portion of thedielectric material 125 in the relief formation 126 is maximal andsubstantially close to 1, while in the external cross section 127, i.e.,close to the upper portion of the hyperfine structure 111, theproportional portion of the dielectric material 128 in the reliefformation 129 is minimal, namely, significantly lower than in material125, and substantially equal to zero.

Typically, when light waves pass through an optical device having aperiodic structure, diffraction of light occurs and the brightness ofthe zero order of the diffracted light, namely, the light which istransmitted through the device without any diffraction, is considerablyreduced. When the pitch of the hyper-fine periodic structure is,however, considerably shorter than the wavelength of the incoming lightwaves, no diffraction occurs. Instead, since the optical waves “see” amedium having a refractive index which is the average of the materialscontained in this medium, effective anti-reflection properties can beobtained.

On the other hand, as illustrated in FIG. 11, when the light waves 130impinge on the periodic hyperfine structure 111 at the upper side of thestructure at oblique angles, they “see” only the external part of theperiodic structure, wherein the proportional part of the transparentmaterial is very low. Therefore, the actual refractive index, which is“seen” by the incoming optical waves, is close to the refractive indexof the air 131.

As a result, and as illustrated in FIG. 12, when such an air-gap film isattached to the external surface 28 of the substrate 20, the coupledlight waves 130 impinge on the interface surface 132 between thesubstrate and the film at angles higher than the critical angle, the air131 confined between the film and the substrate provides an opticalisolation due to the air-like refractive index in the boundary surface.Therefore, the phenomena of total internal reflection of the coupled-inlight waves from the external surface will be preserved and the lightwaves will be contained inside the substrate.

The geometrical characteristic of the hyperfine structure, such as theheight, peak-to-peak and width thereof, can usually be between 10 to 800nanometers. In addition, the exact shape and of the hyperfine structureshould not necessarily be that of the moth eye. Any other nano-structureshape, such as pyramids, prisms, cones and others, can be utilized.Moreover, the hyperfine structure should not necessarily be specificallyperiodic, although a periodic structure is usually easier to fabricate.This hyperfine structure, however, should fulfill the followingrequirements: on one hand, the structure should be solid enough not tocollapse during the attaching process and, on the other hand, theproportional portion of the dielectric material in the externalcross-section of the structure, should be substantially equal to zero,to maintain the total internal reflection phenomena inside thesubstrate. In addition, the size of the basic elements of the hyperfinestructure should not be too large, in order to avoid diffractioneffects. Reducing the thickness of the hyperfine structure to below 100nm, however, might undesirably allow the penetration of the trappedwaves through the air gap film and the deterioration of the totalinternal reflection phenomena. As a result, a typical required value forthe hyperfine structure thickness is between 200 and 300 nm.

FIG. 13a illustrates a front view of an eyeglasses system 140 and FIG.13b a top view of a substrate 20 which is embedded between two opticallenses 141, 142 and assembled inside the eyeglasses frame 143. As seen,in addition to the optical elements, the frame can contain otheraccessories including a camera 144, a microphone 145, earphones 146, USBconnectors, memory cards, an inertial measurement unit (IMU), and thelike.

FIGS. 14a, 14b and 14c illustrate a non-monolithic optical element 150comprising a substrate 20 embedded between front positive lens 151 andrear negative lens 152, mounted together inside a frame 154 withoutadhesive. Air gap films 110 (FIG. 14c ) are placed or bonded between thesubstrate 20 and the lenses 151, 152, wherein the hyperfine structures111, respectively face the external surfaces 26 and 28 of the substrate20. The air gap films 110 can be directly cemented on the planarsurfaces of the optical lenses 151 and 152 using pressure-sensitiveadhesive (PSA), or can be fabricated directly as an integral part of thelenses utilizing embossing, injection molding, casting, machining, softlithography or any other direct fabrication method. The embedded opticalelement 150 can be assembled inside the frame 154 utilizing pressure orcementing techniques.

An alternative method for monolithically embedding the substrate 20between the two optical lenses is illustrated in FIGS. 15a, 15b and 15c. The substrate 20 is embedded between the optical lenses utilizing aperipheral bonding technique. The front lens 151 and rear lens 152 arecemented to the peripheral edges of the substrate 20 using non-opticaladhesive or any other high-viscosity adhesive 156 that mount allcomponents together. The viscosity of the adhesive should be high enoughin order to prevent leakage of the adhesive into the air pockets 131,which are confined between the film 110 and the substrate 20. Such aleakage can eliminate the air gap which is required to preserve thetotal internal reflection of the light waves from the external surfacesof the substrate. The required adhesive 156 can, for example, beOP-67-LS or any room temperature vulcanization (RTV) silicone.

Another alternative method for monolithically embedding the substrate 20between the two optical lenses is illustrated in FIGS. 16a, 16b and 16c. The production procedure of the embedded element is as follows:placing the air gap film 110, with the hyperfine structures 111 facingthe external surfaces 26 and 28 of the substrate 20; utilizing attachingtechniques such as static electricity; preparing a mold 160 having therequired external shape of the element; inserting the substrate 20 intothe mold; casting or injecting the polymer into the mold, curing thepolymer by UV or by changing the polymer temperature, and finally,ejecting the embedded element from the mold. As explained above inrelation to FIGS. 15a to 15c , it is also important that the hyperfineregions will be isolated from the injected material during the injectionmolding process, in order to prevent a leakage of the material into theair pockets 131 between the substrate 20 and the air gap film 110.

FIGS. 13a to 16c illustrate different methods for forming an opticalcomponent comprising a substrate embedded between two optical lenses,however, there are embodiments wherein it is required to attach planarelements to the external surfaces of the substrate. An example for suchan embodiment is illustrated in FIG. 4, wherein the collimating element6 is attached to the substrate 20. Other reasons for attaching a flatelement to a substrate can be for mechanically protecting the substrateto enhance the user's eye-safety, or applying a coating on the externalsurface of the flat element to achieve various characteristics such as,photochromic response, scratch resistance, super-hydrophobicity, tinted(colored) view, polarization, anti-finger print, and the like.

A substrate 20 embedded between two flat substrates 162 and 164 andassembled inside frames 166, 167 is illustrated in FIGS. 17a, 17b and17c . The embedding process of the substrate and the flat substrates 20can be materialized utilizing mechanical attachment, peripheralcementing or monolithic fabrication. Embedding processes can includeattaching only a single element to one of the external surfaces of thesubstrate or combining different elements, such as flat substrates aswell as curved lenses.

In all the embodiments illustrated so far the element for coupling lightwaves out of the substrate is at least one flat partially reflectingsurface located in said substrate, which is usually coated with apartially reflecting dielectric coating and is non-parallel to the majorsurfaces of said substrate. However, the special reflective mechanismaccording to the present invention can be exploited also for othercoupling-out technologies. FIG. 18 illustrates a substrate 20, whereinthe coupling-in element 170 or the coupling-out element 172 arediffractive elements. In addition, other coupling-out elements, such asa curved partially reflecting surface, and other means, can be used.

The embodiments of FIGS. 13-17 are just examples illustrating the simpleimplementation of the present invention. Since the substrate-guidedoptical element, constituting the core of the system, is very compactand lightweight, it could be installed in a vast variety ofarrangements. Many other embodiments are also possible, including avisor, a folding display, a monocle, and many more. This embodiment isdesignated for applications where the display should be near-to-eye;head-mounted, head-worn or head-carried. There are, however,applications where the display is located differently. An example ofsuch an application is a hand-carried device for mobile application,such as, for example, a smartphone or smartwatch. The main problem ofthese smart devices is the contradiction between the required small sizeand volume and the desired high quality image.

FIG. 19 illustrates an alternative method, based on the presentinvention, which eliminates the current necessary compromise between thesmall size of mobile devices and the desire to view digital content on afull format display. This application is a hand-held display (HHD) whichresolves the previously opposing requirements, of achieving small mobiledevices, and the desire to view digital content on a full formatdisplay, by projecting high quality images directly into the eye of theuser. An optical module including the display source 4, the folding andcollimating optics 190 and the substrate 20 is integrated into the bodyof a smart device 210, where the substrate 20 replaces the existingprotective cover-window of the phone. Specifically, the volume of thesupport components, including source 4 and optics 190, is sufficientlysmall to fit inside the acceptable volume for modern smart device. Inorder to view the full screen, transmitted by the device, the window ofthe device is positioned in front of the user's eye 24, observing theimage with high FOV, a large eye-motion-box and a comfortableeye-relief. It is also possible to view the entire FOV at a largereye-relief by tilting the device to display different portions of theimage. Furthermore, since the optical module can operate in see-throughconfiguration, a dual operation of the device is possible; namely thereis an option to maintain the conventional display 212 intact. In thismanner, the standard display can be viewed through the substrate 20 whenthe display source 4 is shut-off. In a second, virtual-mode, designatedfor massive internet surfing, or high quality video operations, theconventional display 212 is shut-off, while the display source 4projects the required wide FOV image into the eye of the viewer throughthe substrate 20. Usually, in most of the hand-carried smart devices,the user can operate the smart device by using a touchscreen which isembedded on the front window of the device. As illustrated in FIG. 19,the touchscreen 220 can be attached to a smart device by directlycementing it on the external surface air gap films 110, which is locatedon the substrate 20.

What is claimed is:
 1. An optical system, comprising: alight-transmitting substrate having at least two external major surfacesand edges; an optical element for coupling light waves into thesubstrate by internal reflection; at least one partially reflectingsurface located in the substrate, for coupling light waves out of thesubstrate; at least one transparent air gap film including a base and ahyperfine structure defining a relief formation, constructed on thebase; wherein the air gap film is attached to one of the major surfacesof the substrate, with the relief formation facing the substratedefining an interface plane, so that the light waves coupled inside thesubstrate are substantially totally reflected from the interface plane.2. The optical system according to claim 1, wherein the air gap filmforms air pockets between the relief formation and the substrate.
 3. Theoptical system according to claim 1, wherein the relief formationincludes dielectric material.
 4. The optical system according to claim1, wherein a proportional portion of the relief formation at a crosssection parallel to the base, gradually changes as a function of thedistance of the cross section from the base.
 5. The optical systemaccording to claim 3, wherein a proportional portion of the dielectricmaterial of the relief formation at an internal cross section close tothe base, is maximal.
 6. The optical system according to claim 3,wherein a proportional portion of the dielectric material of the reliefformation at an internal cross section close to the base, issubstantially equal to one.
 7. The optical system according to claim 3,wherein a proportional portion of the dielectric material of the reliefformation at an external cross section close to the interface plane, isminimal.
 8. The optical system according to claim 7, wherein aproportional portion of the dielectric material of the relief formationat an external cross section close to the interface plane, issubstantially equal to zero.
 9. The optical system according to claim 1,wherein a refractive index of the relief formation at an external crosssection close to the interface plane, is substantially equal to arefractive index of air.
 10. The optical system according to claim 1,wherein the relief formation is a periodic relief formation.
 11. Theoptical system according to claim 1, wherein the relief formation isselected from the group consisting of: (a) a configuration of a motheye, (b) prisms; (c) cones; and (d) pyramids.
 12. The optical systemaccording to claim 1, wherein a geometrical characteristic of thehyperfine structure is selected from the group consisting of: (a)smaller than the wavelength of the incoming light waves; (b) ananostructured film; and (c) between 10 and 800 nanometers.
 13. Theoptical system according to claim 1, wherein the height of the reliefformations less than 1 micron.
 14. The optical system according to claim1, norther comprising at least one optical element having at least oneflat external surface facing the substrate, wherein the base isoptically cemented to the external surface of the element and the reliefformation facing the substrate.
 15. The optical system according toclaim 14, the optical element is a flat transparent substrate.
 16. Theoptical system according to claim 14, wherein the optical element is acollimating module.
 17. The optical system according to claim 14,wherein the optical element is a lens.
 18. The optical system accordingto claim 1, further comprising a second air gap film attached to asecond of the major surfaces of the transparent substrate, with therelief formation facing the substrate surface.
 19. The optical systemaccording to claim 18, further comprising two lenses having each atleast one flat surface, wherein the bases of the first and second airgap films are cemented to the flat surfaces of the lenses.
 20. Theoptical system according to claim 14, wherein the substrate and theoptical element are assembled inside an eyeglasses frame.
 21. Theoptical system according to claim 20, wherein the substrate and theoptical element are mounted together inside the frame without adhesive.22. The optical system according to claim 14, wherein the substrate andthe optical element are embedded together utilizing a peripheral bondingtechnique.
 23. The optical system according to claim 14, wherein thesubstrate and the optical element are monolithically embedded together.24. The optical system according to claim 1, wherein the partiallyreflecting surface for coupling light waves out of the substrate, is aflat surface.
 25. The optical system according to claim 24, wherein thepartially reflecting surface for coupling light waves out of thesubstrate, is coated with a partially reflecting dielectric coating. 26.The optical system according to claim 24, wherein the partiallyreflecting surface for coupling light waves out of the substrate, isnon-parallel to the major surfaces of said substrate.
 27. The opticalsystem according to claim 1, wherein the optical element for couplinglight waves into the substrate by internal reflection, is a diffractiveelement.
 28. The optical system according to claim 1, wherein thepartially reflecting surface for coupling light waves out of thesubstrate, is a diffractive element.
 29. The optical system according toclaim 1, wherein the partially reflecting surface for coupling lightwaves out of the substrate, is a curved surface.
 30. The optical systemaccording to claim 14, wherein the substrate and the optical element areassembled inside a smart device.
 31. The optical system according toclaim 30, wherein the smart device is a smartphone.
 32. The opticalsystem according to claim 30, wherein the smart device is a smartwatch.33. The optical system according to claim 30, wherein the opticalelement is a touchscreen.